The present invention is directed to a direct marking imaging process. Heretofore, a number of patents and publications have disclosed direct marking or acoustically assisted imaging processes, the relevant portions of which may be briefly summarized as follows:
U.S. Pat. No. 2,968,552 to Gundlach, issued Jan. 17, 1961, discloses a method for the simultaneous creation and development of an electric field through changing electric fields in response to a pattern of light and shadow. The invention further discloses the elimination of one or more steps of conventional xerographic operations, specifically cleaning operations necessary for the reuse of the photoconductor. Operation of the invention is accomplished by depositing marking particles on an upper surface of a photoconductor, exposing the particles and photoconductor to a high voltage corona discharge to cause a charge to be deposited on the surface, placing a print receiving pellicle in contact with the surface bearing the particles, and exposing the transparent backing of the photoconductor to a pattern of light and shadow so as to transfer developer material to the print receiving surface.
U.S. Pat. No. 4,833,503 to Snelling, issued May 23, 1989, teaches a multi-color printer employing sonic toner release development. Development is accomplished by vibrating the surface of a toner carrying member and thereby reducing the net force of adhesion of the toner to the surface of the toner carrying member.
U.S. Pat. No. 5,081,500 to Snelling, issued Jan. 14, 1992, discloses an electrophotographic device wherein a vibratory element is employed to uniformly apply vibratory energy to the back side of a charge retentive member having a developed image on the front side thereof. The vibratory energy applied enables the transfer of toner across a gap in those regions characterized by non-intimate contact between the charge retentive member and a copy sheet.
U.S. Pat. No. 5,153,615 to Snelling, issued Oct. 6, 1992, teaches a printing method and apparatus employing a pyroelectric material so as to directly mark an image on a print substrate. The image is produced by locally exposing a uniformly toned pyroelectric member to heat so as to cause the reversal of the charge polarity attracting the toner to the member, and thereby repelling the toner from the toned surface and toward a print substrate in close proximity thereto.
In accordance with the present invention there is provided a method of producing an image on an image receiving member in a direct marking apparatus having an endless photoconductive member with an inner layer, a charge retentive outer layer, and a conductive electrode layer interposed between the inner and outer layers, including the steps of:
(a) uniformly depositing, on an outer surface of the photoconductive member, electrically charged marking particles, said particles being deposited thereon by an electrically biased developer and attracted thereto;
(b) selectively exposing regions of the photoconductive member to a light source so as cause the collapse of the electric field in the exposed regions;
(c) applying an electrical bias to the image receiving member, spaced apart from the outer surface of the photoconductive member, to generate an electric field in a gap between the image receiving member and the photoconductive member; and
(d) applying acoustic energy to the photoconductive member so as to further reduce adhesive forces present between the outer surface of the photoconductive member and the marking particles, said acoustic energy being of sufficient magnitude to enable only the marking particles present on the surface of the photoconductive member in the unexposed regions to be transferred to an outer surface of the image receiving member under the force of the electric field.
In accordance with another aspect of the present invention, there is provided a printing apparatus, comprising:
an endless photoconductive member having an inner layer, a charge retentive outer layer, and a conductive electrode layer between the inner and outer layers;
charged marking particles uniformly deposited on an outer surface of the photoconductive member and held in relative contact therewith;
means for selectively exposing the photoconductive member to light to produce both exposed and unexposed regions therein and to thereby cause the collapse of the electric field in the exposed regions;
an image receiving member, spaced apart from the outer surface of the photoconductive member, for receiving the marking particles, said image receiving member having an electrical bias applied thereto to neutralize an electric field present in a gap between the image receiving member and the exposed regions of the photoconductive member; and
means for applying acoustic energy to the photoconductive member so as to further reduce adhesive forces present between the outer surface of the photoconductive member and the marking particles, said acoustic energy applying means applying acoustic energy having sufficient magnitude to enable only the marking particles present on the surface of the photoconductive member in the unexposed regions to be transferred to an outer surface of the image receiving member.
In accordance with yet another aspect of the present invention, there is provided a multi-color printing apparatus for producing an image on a recording sheet, comprising:
an intermediate member;
a plurality of direct marking devices for depositing marking material on an outer surface of said intermediate member to produce an image thereon, each of said direct marking devices including,
an endless photoconductive member having an inner layer, a charge retentive outer layer, and a conductive electrode layer between the inner and outer layers,
charged marking particles on an outer surface of the photoconductive member and held in relative contact therewith by an electric field created by the charged particles being deposited on the photoconductive member,
means for selectively exposing the photoconductive member to light to produce both exposed and unexposed regions therein and to thereby cause the collapse of the electric field in the exposed regions,
an image receiving member, spaced apart from the outer surface of the photoconductive member, for receiving the marking particles, said image receiving member having an electrical bias applied thereto to neutralize an electric field present in a gap between the image receiving member and the exposed regions of the photoconductive member, and
means for applying acoustic energy to the photoconductive member so as to further reduce adhesive forces present between the outer surface of the photoconductive member and the marking particles, said acoustic energy applying means applying acoustic energy having sufficient magnitude to enable only the marking particles present on the surface of the photoconductive member in the unexposed regions to be transferred to an outer surface of the image receiving member;
a heater, in communication with an internal surface of said intermediate member, for heating said intermediate member so as to cause the tackification of the marking particles deposited on the outer surface thereof; and
means, defining a nip with the outer surface of said intermediate member, for transferring the tackified marking particle image to the recording sheet passing through the nip defined by said intermediate member and said transferring means, whereby the tackified marking particle image is cooled upon contact with the recording sheet to become permanently fixed to the surface thereof.
One aspect of the invention is based on the discovery that the hardware of a direct marking system can be simplified, and system reliability improved by using the vibratory assist techniques described herein. More specifically, the present invention requires no high voltage power supplies, no corona charging devices, no photoreceptor cleaning station or hardware. Furthermore, the present invention enables non-interactive toner deposition so as to allow multi-color images to be produced by a single-pass marking system. This discovery avoids problems that arise in xerographic processes requiring contact between the photoconductor and the surface to which a toner image is to be transferred. The technique described herein is advantageous because it is efficient, simple, and relatively inexpensive compared to other well-known imaging approaches. In addition, it can be used in single color or multiple color printing and reprographic systems. A wide variety of operations can be implemented using these techniques, some of which are described in the embodiments that follow.